(CNN) -- Tropical Storm Emily formed in the Caribbean Monday, prompting area governments to issue warnings and watches, the National Hurricane Center said.

Tropical storm warnings were in effect for Dominica, Puerto Rico, the Dominican Republic and the islands of Guadeloupe, Desirade, Les Saintes and Marie Galante, meaning that tropical storm conditions were expected within 36 hours.

Haiti, the U.S. Virgin Islands and St. Kitts, Nevis, Montserrat and Antigua were under a tropical storm watch. Storm conditions were possible in those areas within 48 hours.

Tropical Storm Emily was located some 105 miles west of Dominica Monday night, according to the hurricane center. It was heading west at 17 miles per hour, packing winds of about 40 miles per hour, with higher gusts. Tropical storm force winds extended outward up to 70 miles.

The center of the storm is expected to move across the northeastern Caribbean Sea Monday night and approach the island of Hispaniola Tuesday night and Wednesday. A long-term forecast from the National Hurricane Center showed the storm could threaten Florida by the weekend.

"This one is pretty vigorous, so we're watching it," said Dennis Feltgen, spokesman for the Miami-based center, before the storm formed.

Aircraft was sent to the area on Monday and was expected to resume reconnaissance work on Tuesday, he said.

"This is a great reminder that we're fast approaching the beginning of the peak of the (hurricane) season," said Feltgen, calling on residents to get prepared now.

Also on Monday, the National Hurricane Center said that Eugene became the fifth hurricane of the eastern Pacific season. Located about 435 miles south-southwest of Manzanillo, Mexico, the Category 1 hurricane is not forecast to hit land.